1. Technical Field
The present invention relates a liquid ejecting apparatus for which countermeasures are taken to prevent liquids from evaporating from nozzles.
2. Related Art
The known liquid ejecting apparatus include an ink jet recording unit (referred to below as a printer) that performs printing by ejecting inks to a recording medium such as printing paper from a recording head (referred to below as a head) used as a liquid ejecting head.
In the printer, an ink is supplied from an ink reservoir such as an ink cartridge or ink tank to an ink chamber in the head. When an actuator, such as a piezoelectric device, provided in the head is driven to increase the pressure of the ink in the ink chamber, the ink is expelled (ejected) from the ink chamber through the opening of a nozzle communicating with the ink chamber.
In this type of printer, the solvent in the ink in the nozzle evaporates through the nozzle opening when power is shut off or the ink is not expelled within a predetermined time. In this case, the viscosity of the ink in the nozzle increases. The nozzle may be clogged with the viscous ink and thereby may fail to expel the ink.
Accordingly, the printer carries out a cleaning process that includes a flushing operation for expelling ink from the nozzle, a suction cleaning operation for forcibly drawing ink from the nozzle, and a sweep cleaning operation for removing ink adhering to a nozzle plane in which the nozzle opening is formed. While no ink is expelled from the nozzle (while power is shut off or the process is not to expel ink), the nozzle plane is covered with a cap member of a capping unit to suppress the solvent in the ink in the nozzle from evaporating.
In the flushing operation, however, which is frequently carried out at periodic intervals, inks are also expelled during printing from nozzles that are not used for the printing, so the amounts of inks used to clean the nozzles not in use during the printing are increased.
Another problem is that even when the nozzle plane is covered with the cap member, a meniscus remains formed in the nozzle and thereby the ink in the nozzle is exposed to the air, according to which the solvent of the ink evaporates through the nozzle opening and the ink in the nozzle easily becomes viscous.
In known methods of preventing an ink from evaporating from a nozzle, an oil is drawn into the nozzle (see JP-A-2009-274418, for example), the nozzle plane is covered with an adhesive layer (see JP-A-2008-307855, for example), and the nozzle is heated to form a drying prevention layer (see JP-A-2008-307708, for example).
In the above methods in which an oil or adhesive, which is a substance other than an ink (a liquid) intended to be ejected, is used, however, the non-ink substance and its storage vessel must be prepared and a specific device to remove the substance from the nozzle plane is also needed. Another problem is that the substance may be mixed with the ink to be ejected. Accordingly, these methods are not practical.
In the method in which the nozzle is heated to form a drying prevention layer, the ink is highly likely to solidify in the nozzle. If the ink solidifies, the solidified ink cannot be ejected by the flushing operation and the suction cleaning operation must be performed, preventing the amount of ink used for nozzle cleaning from being reduced.